In a field of large sized display (in particular, large sized liquid crystal display (LCD)) and organic light emitting diode (MED) display, since power supply lines (i.e., scanning lines) on a backboard have certain resistances and driving currents of all pixels are provided by the power supply lines, a power supply voltage at a region of the backboard closer to a power supply position is higher than the power supply voltage at a region of the backboard far away from the power supply position, this phenomenon is referred to as IR drop. Since a current is related to a voltage, current differences at different regions of the backboard may be caused by IR drop, resulting in mura defects of display.
Currently, main methods in the industry for coping with IR drop are to increase a thickness of a gate metal layer for forming the power supply lines (i.e., scanning lines) or employ a gate metal material having a smaller resistance so as to alleviate an influence of IR drop caused by the formed power supply lines. A general method is to form an ultra-thick (from 6000 Å to 9000 Å) aluminum alloy gate metal layer, wherein, the larger the size of a display panel is, the larger the thickness of the gate metal layer is. However, this method makes great demands on film quality, roughness and etching in subsequent processes of forming an insulating layer and an active layer, and the risk of leakage of electricity is very large. Another general method is to form the gate metal layer with a metal (e.g., copper alloy) having a lower resistance, but this method will result in problems of etching uniformity and cost controlling during a manufacturing procedure of a display panel in a certain specification.